Police arrest 13 in videotaped killings in Nigeria

Story highlights

A video on YouTube that shows a mob killing four students leads to arrests

Graphic video shows bloody victims with tires around their heads

Spokesman says investigators have not yet determined why the mob killed the men

Investigators in Nigeria say they have taken 13 people into custody after a mob attacked four students and burned them alive -- killings that were videotaped and posted online.

A gruesome video on YouTube that showed the killings led to several arrests, police say. The video shows several men on the dirt, writhing in pain. Some are bloodied, and they have tires shoved over their heads.